Why is this happening to me?

Last night was one of the best night I ever had with my 'lil sister... We actually talked for almost 11 hours or so. Anyway, as usual we talked about almost anything we could think of, from our crushes, our family and friends, problems and heartaches. And as usual we also talked about our love for each other. Then she suddenly sat there silently...not talking to me, she just stared at the dark sky. Then after a few minutes she finally said something, "thank you for loving me kahit 'di pwede maging tau " she said.
"Huh? anu na naman yun?" I told her. Finally she told me her problem, the problem that's been eating her up this past few weeks..... "kuya may cyst ako" "I may not live that long and thats why I thanked you" she said with tears welling up in her eyes. I was shocked sa mga sinabi niya..how? paano nya nakuha yun? Why is it that lahat ng taong mahal ko ay kinukuha ng maaga sa akin. I have come to realize that destiny can hurt a person as much as it can Bless them, and I find myself wondering why out of all the people I could have loved, I had to fall for someone destined to be taken away from.... why?